Studies on an organic electroluminescent (EL) element (hereinafter, simply referred to as ‘organic EL element’) have continued from the start point of observing an organic thin film light emission by Bernanose in the 1950s to blue electric light emission using an anthracene single crystal in 1965, and then an organic EL element having a laminated structure which is divided into functional layers of a hole layer and a light emitting layer was proposed by Tang in 1987. Since then, the organic EL element has been developed in a form in which a specific organic material layer is introduced into the element and a specialized material used therefor has been developed in order to improve the efficiency and lifetime of an organic EL element.
In the organic EL element, when voltage is applied between two electrodes, holes are injected into the organic material layer at the anode, and electrons are injected into the organic material layer at the cathode. When the injected holes and electrons meet each other, an exciton is formed, and then the exciton falls down to a bottom state to emit light. Materials used as the organic material layer may be classified into a light emitting material, a hole injection material, a hole transporting material, an electron transporting material, an electron injection material, and the like according to the function.
Light emitting materials may be divided into blue, green, and red light emitting materials according to the light emitting color. In addition, the light emitting materials may be classified into yellow and orange light emitting materials which are necessary for implementing a more natural color. Furthermore, a host/dopant system may be used as a light emitting material for the purpose of enhancing color purity and light emitting efficiency through energy transfer.
Dopant materials may be divided into a fluorescent dopant using an organic material and a phosphorescent dopant using a metal complex compound including heavy atoms such as Ir and Pt. Since the development of the phosphorescent material may theoretically improve light emitting efficiency up to 4 times compared to the fluorescent material, interests in not only phosphorescent dopants, but also phosphorescent host materials have been focused.
As materials used as a hole injection layer, a hole transporting layer, a hole blocking layer, and an electron transporting layer, NPB, BCP, Alq3 and the like represented by the following Formulae have been widely known until now, and for a light emitting material, anthracene derivatives have been reported as a fluorescent dopant/host material. In particular, for the phosphorescent material having a great advantage in terms of improving the efficiency among the light emitting materials, there are metal complex compounds including Ir, such as Firpic, Ir(ppy)3, and (acac)Ir(btp)2, and the compounds are used as blue, green and red dopant materials. Until now, CBP exhibits excellent characteristics as a phosphorescent host material.
However, since the light emitting materials in the related art have a low glass transition temperature and thus are very poor in thermal stability, the materials fail to reach a level which is satisfactory in terms of lifetime for an organic EL element, and need to be improved even in terms of light emitting characteristics. Therefore, there is a need for developing a light emitting material having excellent performance.